How to cut cables for a duplexer

In this video I show the theory and practical methods at determining inter-cavity duplexer lengths.

[@derrick_builds]

Nice. Thanks for sharing. Looking to build a 222 repeater and was surprised when your video nailed what I was looking for.

[@PowderMill]

Thank you so very much! Your videos are outstanding. You are an excellent teacher. I have the Rigol DSA815 and had bought the model with the integrated TG enabled. It’s a nice unit, especially considering the price. It cost me a fraction of the $$ I had spent on my Agilent N9340B w/pre-amp and TG options. I actually take the Rigol out in the field now despite the Agilent being a “ruggedized” “portable” spectrum analyzer. I’d rather break the much more affordable unit. Thanks again for sharing your videos!

[@eie_for_you]

I learned something I had been wondering about! Thanks for adding to my knowledge of duplexers! I have been experimenting with a 440 duplexer I have here on my bench. There appears to be a linear relationship between the frequency of the "secondary dip" and the length of the cable. So, I carefully individually tuned my two cavities to their respective pass frequency. I then installed a "known to be too short" cable between the two cavities. I carefully measured the frequency of the "secondary dip." I then swapped out my "known to be too short" cable for my "known to be too long cable." I carefully measured the frequency of the new secondary dip. Using linear math to create a "y = mx + b" equation [freq = m (cable length in inches) + b], I then predicted the length of cable I needed to put it right on my pass frequency. I installed a cable of that length between the two cavities and ... muy perfecto! Thoughts? This got me within a short distance of the real deal. Turns out this nice linear line warps as it passes the actual pass frequency, so it doesn't get dead on, but it gets you close.

[@chpalmer2007]

Thanks Bryan: Lately at work Ive been taking 6 can notch/pass duplexers from our back room.. taking two cans off the ends and adding full bandpass cans in their place.. to put up on state owned lands as they require the full bandpass on the transmitter. Coming up with the proper lengths for the harness has been totally trial and error.. nice to have the math in hand.

[@seanfinch8011]

Brilliant video Bryan de m0oeg

[@tucontezi]

Learned something, thanks for passing knowledge. Audio was bad though (muffled voice with a lot of ambient noise). A lapel cardioid microphone will work best for this kind of videos. Cheers!

[@TomasRumba]

Excellent just the information I was looking for. How length of the cables and type affects the notch. Thanks my friend. Kp4azh

[@jbx907]

great video, i have a UHF duplexer that does not tune well because of the pigtails, they just made the pigtails without considering measurements. can you do a 430 or 440mhz video.

[@n3sjh]

How do you get 120 degrees for a bandpass cavity?

[@eie_for_you]

The problem I am now having is determining the interconnect between the two duplexer halves to the antenna. An email would be appreciated.

[@skypilot0077]

Great video. The audio is a little weird. Its a bit hard on the ears.

[@user-uv4xe3cq2y]

I don't have great hearing anymore. You sound like you have your microphone in your back pocket and the audio I get is meaningless. Please redo the video with improved/proper audio.

[@chrisscott1547]

Great topic, but audio is very poor.

[@BartKus]

Sinclair says this is not needed. That once you're done your rough tune and put the harness on, all you need to do is putz with the rods a bit. kzbin.info/www/bejne/i2i0i62wd5d_kLc

[@pcr-personalcomputerrepair8844]

sounds 2me like UR using a stereo=microphone OUT OF Phase 180 degrees !!!!

[@ralphpercy4846]

Sound is shit.. must be from radio shack

[@jimromine2917]

Redo the video and this time make the audio so I can hear it

[@W9CR]

Rewatch the video, but pay attention this time.

[@jimromine2917]

@@W9CR hard to pay attention when audio is so bad